The Astounding Magnetic Sensor in the Human Eye

In A Nutshell

Birds, sea turtles, bats, and an assortment of other animals have the ability to navigate by sensing the Earth’s magnetic field, yet it’s long been assumed humans are devoid of this skill—after all, we do have an ungainly habit of getting lost in the woods. However, researchers have recently discovered that humans have the same magnetic-sensing protein in our eyes that’s found in all types of other animals. How, exactly, we’re using that protein is still unclear.

The Whole Bushel

Animals sense magnetic fields in a variety of ways and one of those ways is by using an eye protein called cryptochrome, which uses light to detect the tiniest of geomagnetic differences. Migratory birds, fruit flies, and butterflies are known to rely on this protein to accurately get where they’re going, and, surprisingly, the human eye contains cryptochrome too. Of course, this raises the question: If we have magnetic sensors in our eyes, why are we buying pricey GPS navigators and still managing to get hopelessly turned around? Well, it turns out, scientists aren’t entirely sure.

What we do know is that if you “knock out” a fruit fly’s magnetic sensing gene and then replace it with human cryptochrome, the fruit fly’s geomagnetic vision is restored. Scientist Steven M. Reppert and his colleagues discovered this after first swapping cryptochrome in monarch butterflies and fruit flies. Being able to seamlessly switch the fruit fly cryptochrome for the butterfly version let the researchers know that both animals were using the protein for the same purpose—magnetic navigation. Then, after noticing the remarkable DNA similarities between monarch and human cryptochromes, they decided to see if the eye protein from people would also work in the fruit flies. And it did.

Reppert’s findings don’t prove we have some kind of latent or unknown magnetic sense, but he did conclude his study by saying, “A reassessment of human magnetosensitivity may be in order.”

Before Reppert’s work, no one had done any significant research in human magnetoreception since the 1980s when Dr. Robin Baker of the University of Manchester performed a series of experiments suggesting people can indirectly sense magnetic fields. In his experiments, he would get blindfolded volunteers, take them on long, convoluted journeys, and then ask them to point their way back home. He performed the study on thousands of participants and found that most people could point in the correct direction. The only time their accuracy dropped was when they wore magnets on their heads. Unfortunately, no one other than Baker has been able to repeat his study and get the same results. Consequently, Baker’s human magnetoreception findings were heavily ridiculed, and he eventually moved on to other research. The new information about cryptochromes, however, is causing some to give Baker’s work another look.

Previously, it was thought people used cryptochromes strictly for maintaining our bodies’ circadian rhythms, yet now some are wondering if it might also work as an optical compass. Perhaps we are better navigators than we thought but aren’t utilizing our full capabilities. Or maybe, a long, long time ago humans did use geomagnetic orientation and somehow lost the skill through evolution, or our modern, electromagnetic world is blocking our abilities. The most likely and commonly accepted explanation is that humans might simply use cryptochrome in a different way than fruit flies and butterflies. Maybe so, but that common sense hypothesis won’t stop us from trying to unleash our Magneto-like superpowers.